YANGON, Myanmar — At least 24 people were believed on Monday to have died in western Myanmar after unknown assailants attacked police outposts on Sunday near the border with Bangladesh.

In Maungdaw, a township in Rakhine State close to the border, seven villagers, all members of the Rohingya Muslim minority, were said to have been shot to death when joint army and police forces began a counteroperation on Monday.

About a million Rohingya live in the area and are officially stateless, having been denied citizenship by the Myanmar authorities who refuse to even use the term Rohingya, saying the people are actually Bengalis from Bangladesh.

“This morning about 6 a.m., the security forces, loaded onto three trucks, arrived in Myothugyi village, a mile east of Maungdaw town, and seven people were gunned down,” U Zaw Oo, a Rohingya in Maungdaw, said by telephone on Monday.

“The situation in the town is quiet, and all Muslim residents here are just staying at home since we are very scared of the security forces,” he added.

Another Rohingya Muslim, Hafizul, a volunteer with an international humanitarian organization who, like many Rohingya, uses just one name, said that, because villagers feared the police and soldiers, those who were killed on Monday had been attempting to flee after security forces entered the village. He said the soldiers had arrived on Sunday to assist the police.

A local journalist who was with the security forces in the village also said that shooting had occurred. “Three suspects were killed as they ran away when the security forces entered the village,” Mratt Kyaw Thu, a reporter with Frontier Myanmar, said on Monday.

When a senior press officer for Rakhine State, U San Nwe, was asked about the events, he declined to comment.

The violence on Monday occurred a day after dawn attacks on three outposts of the Myanmar border police by unidentified militants. Myanmar’s police chief, Maj. Gen. Zaw Win, said that nine police officers were “brutally killed” during “terror attacks” on Sunday and that eight militants had been killed. The police said the attackers had made off with 62 assorted weapons and 10,130 rounds of ammunition during the attacks.

“The attackers used swords, spears and homemade weapons,” General Zaw Win said during a news conference in the capital, Naypyidaw, on Sunday evening.

He did not identify the attackers as members of any particular organization. But he said they “shouted ‘Rohingya! Rohingya!’ and they used Bengali language.”

After the bloodshed on Sunday, the government imposed a curfew of 7 p.m. to 6 a.m. and declared a state of emergency in Maungdaw and in three other townships.

The police and other official sources in Rakhine State posted gruesome photographs of the bodies of some officers and attackers on social media, saying the throats of some of the officers had been slit.

Western Myanmar and the plight of the Rohingya received international attention in June 2012 as more than 300 were killed and hundreds of thousands were affected by sectarian violence set off by the rape and killing of a Buddhist woman in Rakhine State.

The latest violence is the worst sectarian problem to face the government led by Daw Aung San Suu Kyi since it took office in March. In September, Ms. Aung San Suu Kyi formed an advisory commission on Rakhine State under the chairmanship of the former United Nations secretary general, Kofi Annan. After the attacks on Sunday, she told government officials that the matter had to be dealt with by law enforcement, according to the information minister, U Pe Myint.

Human Rights Watch expressed its concern that the attacks on the police posts and the counteroperation by security forces would create chaos in western Myanmar.

“The army and police should ensure full troop discipline in its operations, as there are frequent reports of rights abuses by police units against the Rohingya population,” said David S. Mathieson, a senior researcher for Human Rights Watch on Myanmar, formerly known as Burma.

He added: “The search for perpetrators cannot descend into abuses of a local population already suffering under sharp restrictions on freedom of movement, work and access to services.”